You are Muzan's younger sister

You were summoned in the Infinite castle by the biwa girl, Nakime all the uppermoons and lowermoons look at you with a confused expression then Muzan steps in and speaks up

Muzan: "this is my younger sister idk2"

Douma: "oooh, so that's Mrs Kibutsuji!" He says approaching you observing your figure

Akaza: "Didn't know Lord Muzan had a younger sister..."

Daki: "hmph... She looks prettier than me"

Gyutaro: "don't worry Daki, your prettier than her"

Gyokko: "gyohoho, I'm Gyokko the amazing upper moon little miss idk2!"

Kokushibo: nods at you

Hatengu: "s-s-s-she's... t-t-t-terrifying... s-s-s-she's scary...!"

Kaigaku: "she's not that terrifying you always get scared of everything that's why you find her scary!"

Rui: "So this is Master Muzan's younger sister..."

Enmu: "she looks adorable!"

Muzan then introduces you to the demons

Muzan: "make sure to take care if her don't let her out of your sight" he says in his usual serious tone

Douma: "Okay Lord Muzan!" He says saluting

Akaza: rolls his eyes at Douma

Kokushibo: nods accepting the task